The present invention relates generally to devices and methods for driving reactive loads, and more specifically to a highly efficient power amplifier configured to drive capacitive loads. The present invention can be optimized for use in a parametric loudspeaker system.
U.S. Pat. No. 6,661,285 (the “'285 patent”) issued Dec. 9, 2003 entitled POWER EFFICIENT CAPACITIVE LOAD DRIVING DEVICE discloses a general purpose power-efficient driver for reactive, usually capacitive, loads that employs a switching scheme to deliver power to the load. The power-efficient driver disclosed in the '285 patent may be employed in a parametric audio system that includes a modulator for modulating an ultrasonic carrier signal with an audio signal, a driver amplifier for amplifying the modulated ultrasonic signal, and one or more acoustic transducers (e.g., capacitive transducers) configured to receive the amplified ultrasonic signal and project it through the air along a selected path. Because of the non-linear propagation characteristics of the air, the modulated ultrasonic carrier signal is demodulated as it passes through the air, thereby regenerating the audio signal along the selected path of projection. As disclosed in the '285 patent, the switching scheme includes a plurality of switches that can be arranged in an “H-bridge” or any other suitable arrangement, and the control scheme for the switches can be optimized with regard to desired signal characteristics and design goals, which are generally to maximize accuracy of the intended signal and to minimize power consumption. The capacitive load driving device disclosed in the '285 patent may be employed in a number of applications such as sonar control systems, RF transmission systems, parametric audio systems, etc.
Although the capacitive load driving device disclosed in the '285 patent has been successfully employed to drive capacitive loads in a more power efficient manner, it would be desirable to have an improved capacitive load driving device and method that provides increased signal voltage gain, over-voltage, over-current, and over-temperature protections, over-modulation prevention, output level control, minimized harmonic generation, and compensation for propagation medium distortion.